Cryocoolers are devices that provide cooling (removal of heat) to very low temperatures. Common cryocoolers are either single-stage where the cryocooler can cool a given component of a device to 30 K, or two-stage, cooling the component to lower than 30 K, often preferably to less than 10 K. There are various types of two-stage cryocoolers, for example Gifford-McMahon (GM) or Pulse Tube, with varying cooling power capacities. Two-stage cryocoolers may be used to cool and keep cool superconducting magnets. A typical cryocooler may be viewed as being comprised of two pieces of hardware, the cryohead (or cold head) and the compressor that are connected by a pair of flexible high pressure hoses. The cryohead is the hardware that is directly attached to the target device to be cooled. In the so called “conduction-cooled” superconducting magnets, heat removal by the cryohead is achieved inside a vacuum chamber, commonly called a cryostat, through conduction by means of physical contacts with the target components of the superconducting magnet such as the coil assembly. FIG. 1 represents the design of a common two-stage GM cryohead 10 that can cool a device to less than 30 K. Notable features of the cryohead 10 are the room temperature flange 100 that connects the cryohead to the room temperature body of a given cryostat, first-stage flange 110 that connects to certain parts of a cryostat that needs to be cooled to and maintained at 30-80 K, often the radiation shield, and second-stage flange 120 often referred to as the cold finger, that connects to a certain part of a device, such as coil assembly of a superconducting magnet, that needs to be cooled to and maintained at less than 30 K. The first-stage 110 and the second-stage 120 of the type of cryohead shown in FIG. 1, that can be used to cool a conduction-cooled superconducting magnet, is commonly housed inside the vacuum space of the cryostat of the superconducting magnet system, other portion of the cryohead is located outside the cryostat where auxiliary hoses and wires are connected to the cryohead. Heat extraction, also known as heat rejection, is often by way of individual couplings, or joints, or links that are bolted, fitted, bonded, or clamped to the first-stage and second-stage flanges, but may be mechanically or metallurgically connected otherwise.
This disclosure relates to how mechanical connections may be made at the first-stage and/or second-stage, or other stages, of a cryohead. Installation of a cryohead of the type shown in FIG. 1 in a conduction-cooled device, such as a conduction-cooled superconducting magnet, requires mechanical attachments to all three flanges. The disclosure teaches the design and use of certain couplings at the first-stage and the second-stage of the cryohead that allow the cryohead to be installed on a device to be cooled by first inserting the cryohead into the cryostat of a device whereby the process of insertion causes socket-like parts of the individual couplings that may be attached to the first-stage and the second-stage flanges to engage the post-like parts of the couplings that may be connected to target components of the device and second connecting the room temperature flange of the cryohead to the room temperature body of the cryostat. The process of insertion causes mechanical engagements by sliding of the socket parts over post parts. Once the cryohead is installed and when the cryohead starts the cooling process the socket parts, that are made from materials that as a whole contract more than the materials of the post, contract and compress over the post parts and produce mechanical-thermal connection desired for good conduction cooling. Those knowledgeable in the art are aware that connection of the cryohead to the room temperature body of the cryostat involves use of various combinations of o-rings, bellows, and various other vacuum fittings, which are not discussed in this disclosure. While the text of this disclosure general applies to mechanical connections at all cooling stages, in this disclosure often we address an embodiment of a mechanical connection made at the second-stage of a two-stage GM cryocooler as an example.